Can't dynamically set array initializer length

Question

I am using C# to hook into the FedEx API and I'm a bit stumped on how to modify some existing code to meet my needs. The snippet included is part of their canned code where they sample how to work with 1 commodity. However, when my code runs I will have n commodities...and I'm unsure how to dynamically address this.

As an example, if I have 3 commodities, and I manually add 3 new Commodity() statements it will work fine. However this needs to be dynamic.

request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[3] { 
  new Commodity(), 
  new Commodity(), 
  new Commodity() 
};

Here is the start of the method, where the first line is what I need help with. After that I think putting everything else in a loop based on array size should be fine.

request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[1] { 
  new Commodity() 
};

request.RequestedShipment.CustomsClearanceDetail.Commodities[0].NumberOfPieces = "1";
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Description = "Books";
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].CountryOfManufacture = "US";
//
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Weight = new Weight();
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Weight.Value = 1.0M;
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Weight.Units = WeightUnits.LB;

If I simply do this, I get an error:

request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[3] { 
  new Commodity() 
};

"An array initializer of length 3 is expected"

Why not put `[]` i.e. `request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[] { new Commodity() };` and let system derive the actual size — Dmitry Bychenko, Jun 13 '19 at 11:54
Thanks for the reply, however when I do this and run it through a loop for 3 commodities it works fine for array position 0. When it gets to position 1 I get System.IndexOutOfRangeException: 'Index was outside the bounds of the array.' — user1134307, Jun 13 '19 at 12:07
do not *hardcode* indexes: `Commodities[1]` i.e. commodity **#2** will throw exception if you have just **1** commodity in the array. What is your loop, then? — Dmitry Bychenko, Jun 13 '19 at 12:12

Dmitry Bychenko · Accepted Answer · 2019-06-13T12:10:20.803

First, you don't have to mention 1 or 3 at all; put [] and let system compute the required length for you:

// Commodity[3] will be created
request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[] { 
  new Commodity(), 
  new Commodity(), 
  new Commodity() 
};

Or

// Commodity[1] will be created
request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[] { 
  new Commodity()
};

If you want to create an array of size n, you can try Linq:

using System.Linq;

...

int n = 3;

request.RequestedShipment.CustomsClearanceDetail.Commodities = Enumerable
  .Range(0, n) 
  .Select(index => new Commodity())
  .ToArray();

Or even

int n = 3;

// 3 equivalent commodities
request.RequestedShipment.CustomsClearanceDetail.Commodities = Enumerable
  .Range(0, n) 
  .Select(index => new Commodity() {
     NumberOfPieces = "1", 
     Description = "Books",
     CountryOfManufacture = "US",
     Weight = new Weight() {
       Value = 1.0M,
       Units = WeightUnits.LB
     }
   })
  .ToArray();

Your first Linq example works like a champ, thank you! – user1134307 Jun 13 '19 at 12:17 — user1134307, Jun 13 '19 at 12:17

score 0 · Answer 2 · answered Jun 13 '19 at 12:19

@Dmitry Sir, covered almost everything in above answer... However, below section can also be written as followed section:

Your original code

request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[1] { 
  new Commodity() 
};

request.RequestedShipment.CustomsClearanceDetail.Commodities[0].NumberOfPieces = "1";
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Description = "Books";
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].CountryOfManufacture = "US";
//
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Weight = new Weight();
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Weight.Value = 1.0M;
request.RequestedShipment.CustomsClearanceDetail.Commodities[0].Weight.Units = WeightUnits.LB;

It can be modified as below:

Modified dynamic len array and property initialized code

request.RequestedShipment.CustomsClearanceDetail.Commodities = new Commodity[] { 
   new Commodity {
      NumberOfPieces = "1",
      Description = "Books",
      CountryOfManufacture = "US",
      Weight = new Weight{
            Value = 1.0M,
            Units = WeightUnits.LB
      },
      // add more properties... as per requirement
   },
   // add more objects... as per requirement
};

Can't dynamically set array initializer length

2 Answers2